Measurement device

Abstract

A measurement device is for use with a current-type sensor unit, which, when applied with a driving voltage, is capable of reacting with a target substance for generating a sensor current that corresponds to a concentration level of the target substance, and includes: a driving unit operable to generate the driving voltage that includes alternating current (AC) and direct current (DC) components; and a processing unit for receiving the sensor current from the current-type sensor unit, and operable to determine the concentration level of the target substance according to a peak-to-peak value of the sensor current received by the processing unit.

What is claimed is: 
     
       1. A measurement device adapted for use with a current-type sensor unit, which, when applied with a driving voltage, is capable of reacting with a target substance for generating a sensor current that corresponds to a concentration level of the target substance, said measurement device comprising:
 a driving unit configured to generate the driving voltage that includes an alternating current (AC) component and a direct current (DC) component, and adapted to be connected electrically to the current-type sensor unit for providing the driving voltage to the current-type sensor unit; and 
 a processing unit adapted to be connected electrically to the current-type sensor unit for receiving the sensor current from the current-type sensor unit, and configured to determine the concentration level of the target substance according to a peak-to-peak value of the sensor current received by said processing unit; 
 wherein said processing unit includes:
 a signal amplifying circuit adapted to be connected electrically to the current-type sensor unit for receiving the sensor current from the current-type sensor unit, and configured to convert the sensor current into a sensor voltage; and 
 a signal processing circuit connected electrically to said signal amplifying circuit for receiving the sensor voltage from said signal amplifying circuit, and configured to determine the concentration level of the target substance according to a peak-to-peak value of the sensor voltage, to determine a peak-to-peak value of a correction current according to the peak-to-peak value of the sensor voltage and a predetermined correction value, and to subsequently determine the concentration level of the target substance according to a result of division of the peak-to-peak value of the correction current by a predetermined sensitivity value. 
 
 
     
     
       2. The measurement device as claimed in  claim 1 , wherein said driving unit includes a series connection of a power supply and a signal generator that cooperate to generate the driving voltage, and that respectively contribute to the DC component and the AC component of the driving voltage. 
     
     
       3. The measurement device as claimed in  claim 1 , wherein said signal processing circuit is configured to determine the peak-to-peak value of the correction current based on an average of the peak-to-peak value of the sensor voltage during each cycle within a predetermined time after said driving unit starts providing the driving voltage to the current-type sensor unit. 
     
     
       4. The measurement device as claimed in  claim 1 , the current-type sensor unit including input and output electrodes for receiving the driving voltage and outputting the sensor current therethrough, respectively, wherein:
 said driving unit is adapted to be connected electrically to the input electrode for providing the driving voltage to the current-type sensor unit therethrough; and 
 said signal amplifying circuit includes a resistor, and 
 an operational amplifier having a first input terminal that is adapted to be connected electrically to the output electrode for receiving the sensor current from the current-type sensor unit, a grounded second input terminal, and an output terminal that is connected electrically to said first input terminal via said resistor and that is connected electrically to said signal processing circuit, said operational amplifier being configured to generate the sensor voltage based on the sensor current received by said operational amplifier for output to said signal processing circuit via said output terminal. 
 
     
     
       5. The measurement device as claimed in  claim 4 , wherein said second input terminal of said operational amplifier is a non-inverting input terminal, and the driving voltage generated by said driving unit is a positive voltage relative to said second input terminal of said operational amplifier. 
     
     
       6. The measurement device as claimed in  claim 1 , wherein said processing unit further includes a filter connected electrically between said signal amplifying circuit and said signal processing circuit for removing frequency components, that do not correspond to the AC component of the driving voltage, from the sensor voltage received by said signal processing circuit.